The legendary Ted Williams once said that squarely hitting a round baseball with a round bat is the hardest thing to do in all of sports, and he said that before the age of one-inning relievers and sliders that have velocity and movement. Now, imagine trying to hit Andrew Miller or Clayton Kershaw or Noah Syndergaard while also dealing with an ache or pain that prevents you from being at your best.

Yet, we know that hitters are trying to do this all the time. And while there's a certain virtue to showing up every day and trying to play through pain, particularly in terms of gaining clubhouse respect, players can hurt their teams when they're so limited that they just can't play to their usual potential.

Gregory Polanco is shaken up after fouling a ball off his knee in the top of the 6th inning, but remains in the game

Let's provide a short list of Polanco's 2016 injuries, shall we? Between right shoulder discomfort, a sore left hamstring, left foot pain, and a bruised face, it was a tough year, and he reportedly also received a PRP injection in his left knee and left shoulder in October. It's not hard to see how that all took a toll on him as the year went on, because after putting up a first half that was basically the breakout we all expected (.287/.362/.500, 128 wRC+, which is Manny Machado production), his second half was a mess (.220/.267/.414, 80 wRC+).

Check out his 20-game rolling exit velocity chart, to see this in action. The first half shows pretty consistent production, but the second is an up-and-down mess of peaks and valleys, and that actually started in late June, when "leg soreness" kept him out of an series against the Dodgers.

Gregory Polanco dealt with a series of injuries in 2016 that affected his hitting.

Despite that, Polanco's overall 2016 line (.258/.323/.463, 108 wRC+) was his best, in part because he followed the Daniel Murphy strategy of pulling the ball in the air more than ever. If he can stay whole in 2017, he could be the best hitter in a stacked Pittsburgh outfield.

Carlos Correa twists his left ankle as he steps on first base running out a ground ball and is forced to leave the game in the 5th inning

Like Polanco, Correa had a good year, overall. In his age-21 season, he hit .274/.361/.451 (122 wRC+) with 20 homers, and he could merely just do that every year and be a star. But his power was down from his 2015 debut, when he hit two more homers in 228 fewer plate appearances.

Can we see the same effect in exit velocity as we did with Polanco? We sure can.

It's not hard to see how injuries affected Carlos Correa in 2016.

We should caution, however, that Correa wasn't exactly lighting it up before the ankle injury -- .256/.351/.423 is good, not elite -- so it's not entirely about the injuries. They certainly didn't help, though.

The Nationals' trainer checks on Bryce Harper after he swings and misses at a pitch, and Harper later exits the game with a stiff neck

We're nearing an endless amount of words being written on how Harper's smashing April (.286/.406/.714) turned into a frustratingly average hitter for the remaining five months, particularly since there was never a satisfying answer as to why. There were multiple reports of Harper dealing with neck/shoulder issues, particularly when he took a week off in August.

We can't say with certainty that this is a case of injury, but it's truly difficult to believe that a hitter as great as he was in 2015 and early 2016 could simply fall off that badly without some sort of physical issue. Instead of using exit velocity this time, let's reach back to a September article that used Statcast™ defensive positioning data:

Yes, we know that the Twins surprisingly designated Park for assignment on Friday, but some team will probably take a gamble on him, and we just used Statcast™ to explain why earlier this week. The takeaway there is that while Park did indeed have contact issues, he was among the most elite hitters in baseball in terms of making hard contact, and he did it with a nagging right wrist injury that required surgery. Some team will be interested in finding out what he can do when healthy, and the risk is low.

Lost in the wreckage of Conforto's disappointing 2016 was that he actually got off to a tremendous start, hitting .365/.442/.676 in April and looking every bit the star that he was expected to be after his 2015 debut. It didn't work out that way, of course, as he ended up being demoted to Triple-A and is slated to start 2017 on the bench. But did you remember that in mid-June, his left wrist was sore enough that he received a cortisone shot?

We don't know exactly when the wrist soreness first popped up, but we do know his exit velocity was 92.6 mph in April, and 90.4 mph afterward. There's lot of reasons that could be, of course, including the league adjusting to a young hitter who couldn't adjust back.

Marcell Ozuna has to exit the game in the bottom of the 4th inning with a sore left wrist after his amazing catch one inning earlier

But in Ozuna's case, the exit velocity didn't change all that much. Instead, he hit more ground balls in the second half, jumping from 42 percent to 46 percent, including a whopping 54 percent grounder rate in August. That's exactly what his problem had been in 2015 -- hard-hit grounders that didn't lead to production. We're speculating that this is because of the wrist issues, because we can't say we know for sure. It makes plenty of sense, though, doesn't it? The Ozuna we saw to begin 2016 was exactly the star we'd expected to see.

Mike Petriello is an analyst for MLB.com and the host of the Statcast podcast. He has previously written for ESPN Insider and FanGraphs. This story was not subject to the approval of Major League Baseball or its clubs.